In recent years, a control device for controlling a throttle valve mounted in an engine of an automobile is provided with a system for controlling an opening of a throttle valve in response to an electric control signal based on the amount of depression of an accelerator pedal (accelerator pedal position). Such a system is called drive-by-wire (DBW) control system.
A known example of the control device, which is constructed in the simplest form as shown in FIG. 6, is adapted to transmit a control signal which fully represents or corresponds to the amount of depression of the accelerator pedal (accelerator pedal position). In this case, the control device principally consists of a sensor (accelerator position sensor) 10 for detecting the amount by which the accelerator pedal is depressed by a driver, a motor (throttle actuator) 20 for driving the throttle valve, and a driver-by-wire control unit 30 for converting a signal (indicative of the accelerator pedal position) received from the accelerator position sensor 10, into a corresponding drive signal used for driving the motor 20.
Another known example of the control device, which is in FIG. 7, includes an electronic control unit (ECU) 40 in addition to the above-described components 10-30, and is capable of driving the throttle valve with higher accuracy. In this example, the ECU 40 sets a target throttle opening (target TPS), based on a pseudo accelerator pedal position obtained by correcting a signal (indicative of an accelerator pedal position) from the accelerator position sensor 10 in accordance with operating conditions of the engine and other information. The drive-by-wire control unit 30 converts an output signal of the ECU 40 representing the target throttle opening TPS, into a drive signal to be transmitted to the motor 20.
If the ECU 40 is interposed between the accelerator position sensor 10 and the drive-by-wire control unit 30, the throttle valve can be driven more appropriately, but a delay arises in the response of the throttle opening to the current position of the accelerator pedal, due to computing time taken by the ECU 40 to compute the target throttle opening TPS, and time required for transmitting signals between the ECU 40 and the drive-by-wire control unit 30 and between the ECU 40 and the accelerator position sensor 10. This may make a driver feel uncomfortable when he/she depresses the accelerator pedal (namely, when the vehicle is accelerated), for example.
Japanese laid-open Patent Publication (Kokai) No. 3-141839 discloses a technique for deriving the target throttle opening directly from the amount of depression of the accelerator pedal when the engine is in a non-loaded state, thereby to solve the problem of racing of the engine. Japanese laid-open Patent Publication (Kokai) No. 3-290027 discloses a technique for setting the target throttle opening to an appropriate value so as to achieve an effective engine brake. These techniques, however, cannot solve the above-described problem of the delay in the response.